Hydrogen sulfide (H2S) is a deadly gas that causes asphyxiation, lung damage, and teratogenic effects when humans or animals are exposed to it (1-2). H2S gas is encountered widely in sources such as natural gas and petroleum, in mines, and as a by-product in the manufacture of rayon, synthetic rubber, and dyes, as well as in the tanning of leather (3-4). Thus, the monitoring and elimination of hydrogen sulfide is very important for safety. Up to now, a variety of inorganic and organic materials, such as tungsten oxide, tin oxide, and carbon have been proposed as electrical sensors that can detect H2S gas (5-11). Drawbacks of existing H2S monitors include high power consumption, high required operating temperatures, short lifetime, interference from other gases, and high cost (12). Many other chemical agents are encountered during petroleum extraction or mining operations that are either dangerous or corrosive, and whose detection by chemical sensors is desirable.
There has been significant interest in using carbon-based nanomaterials as chemical sensors due to advantages such as light weight, high electrical conductivity, high electrochemical surface area, and superior sensing performance. Carbon nanotubes (CNT), including single-walled carbon nanotubes (SWCNT), are particularly attractive due to their high electron mobility and large current carrying capacity. CNT can reduce power consumption and exhibit high temperature stability and chemical inertness, providing a stable and robust platform to detect specific analytes, such as gases (13-20). Chemical sensors containing untreated CNTs utilize their intrinsic electrochemical properties, which limits the sensor selectivity and sensitivity. One approach has been to functionalize CNTs either covalently or non-covalently with various materials (21-24). However, owing to their one-dimensional nanostructure, CNTs are highly sensitive to environmental factors such as humidity and temperature (25-26), which can restrict their use depending on the season, region, and weather. Thus, there is a need for more selective, specific, and stable nanoscale and microscale chemical sensor devices and methods for making and using them.